Google Git
Sign in
gnu / gcc / 96e055f719ec2f88fb47185ae05eea5c752bd0fd / . / gcc / gcc.info-26
blob: 340acc63b377458423a4c46094b97de14fa81a4a [file] [log] [blame]
This is Info file gcc.info, produced by Makeinfo version 1.68 from the
input file gcc.texi.
This file documents the use and the internals of the GNU compiler.
Published by the Free Software Foundation 59 Temple Place - Suite 330
Boston, MA 02111-1307 USA
Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998
Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the sections entitled "GNU General Public License," "Funding for
Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are
included exactly as in the original, and provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the sections entitled "GNU General Public
License," "Funding for Free Software," and "Protect Your Freedom--Fight
`Look And Feel'", and this permission notice, may be included in
translations approved by the Free Software Foundation instead of in the
original English.

File: gcc.info, Node: Misc, Prev: Cross-compilation, Up: Target Macros
Miscellaneous Parameters
========================
Here are several miscellaneous parameters.
`PREDICATE_CODES'
Define this if you have defined special-purpose predicates in the
file `MACHINE.c'. This macro is called within an initializer of an
array of structures. The first field in the structure is the name
of a predicate and the second field is an array of rtl codes. For
each predicate, list all rtl codes that can be in expressions
matched by the predicate. The list should have a trailing comma.
Here is an example of two entries in the list for a typical RISC
machine:
#define PREDICATE_CODES \
{"gen_reg_rtx_operand", {SUBREG, REG}}, \
{"reg_or_short_cint_operand", {SUBREG, REG, CONST_INT}},
Defining this macro does not affect the generated code (however,
incorrect definitions that omit an rtl code that may be matched by
the predicate can cause the compiler to malfunction). Instead, it
allows the table built by `genrecog' to be more compact and
efficient, thus speeding up the compiler. The most important
predicates to include in the list specified by this macro are
thoses used in the most insn patterns.
`CASE_VECTOR_MODE'
An alias for a machine mode name. This is the machine mode that
elements of a jump-table should have.
`CASE_VECTOR_PC_RELATIVE'
Define this macro if jump-tables should contain relative addresses.
`CASE_DROPS_THROUGH'
Define this if control falls through a `case' insn when the index
value is out of range. This means the specified default-label is
actually ignored by the `case' insn proper.
`CASE_VALUES_THRESHOLD'
Define this to be the smallest number of different values for
which it is best to use a jump-table instead of a tree of
conditional branches. The default is four for machines with a
`casesi' instruction and five otherwise. This is best for most
machines.
`WORD_REGISTER_OPERATIONS'
Define this macro if operations between registers with integral
mode smaller than a word are always performed on the entire
register. Most RISC machines have this property and most CISC
machines do not.
`LOAD_EXTEND_OP (MODE)'
Define this macro to be a C expression indicating when insns that
read memory in MODE, an integral mode narrower than a word, set the
bits outside of MODE to be either the sign-extension or the
zero-extension of the data read. Return `SIGN_EXTEND' for values
of MODE for which the insn sign-extends, `ZERO_EXTEND' for which
it zero-extends, and `NIL' for other modes.
This macro is not called with MODE non-integral or with a width
greater than or equal to `BITS_PER_WORD', so you may return any
value in this case. Do not define this macro if it would always
return `NIL'. On machines where this macro is defined, you will
normally define it as the constant `SIGN_EXTEND' or `ZERO_EXTEND'.
`SHORT_IMMEDIATES_SIGN_EXTEND'
Define this macro if loading short immediate values into registers
sign extends.
`IMPLICIT_FIX_EXPR'
An alias for a tree code that should be used by default for
conversion of floating point values to fixed point. Normally,
`FIX_ROUND_EXPR' is used.
`FIXUNS_TRUNC_LIKE_FIX_TRUNC'
Define this macro if the same instructions that convert a floating
point number to a signed fixed point number also convert validly
to an unsigned one.
`EASY_DIV_EXPR'
An alias for a tree code that is the easiest kind of division to
compile code for in the general case. It may be `TRUNC_DIV_EXPR',
`FLOOR_DIV_EXPR', `CEIL_DIV_EXPR' or `ROUND_DIV_EXPR'. These four
division operators differ in how they round the result to an
integer. `EASY_DIV_EXPR' is used when it is permissible to use
any of those kinds of division and the choice should be made on
the basis of efficiency.
`MOVE_MAX'
The maximum number of bytes that a single instruction can move
quickly between memory and registers or between two memory
locations.
`MAX_MOVE_MAX'
The maximum number of bytes that a single instruction can move
quickly between memory and registers or between two memory
locations. If this is undefined, the default is `MOVE_MAX'.
Otherwise, it is the constant value that is the largest value that
`MOVE_MAX' can have at run-time.
`SHIFT_COUNT_TRUNCATED'
A C expression that is nonzero if on this machine the number of
bits actually used for the count of a shift operation is equal to
the number of bits needed to represent the size of the object
being shifted. When this macro is non-zero, the compiler will
assume that it is safe to omit a sign-extend, zero-extend, and
certain bitwise `and' instructions that truncates the count of a
shift operation. On machines that have instructions that act on
bitfields at variable positions, which may include `bit test'
instructions, a nonzero `SHIFT_COUNT_TRUNCATED' also enables
deletion of truncations of the values that serve as arguments to
bitfield instructions.
If both types of instructions truncate the count (for shifts) and
position (for bitfield operations), or if no variable-position
bitfield instructions exist, you should define this macro.
However, on some machines, such as the 80386 and the 680x0,
truncation only applies to shift operations and not the (real or
pretended) bitfield operations. Define `SHIFT_COUNT_TRUNCATED' to
be zero on such machines. Instead, add patterns to the `md' file
that include the implied truncation of the shift instructions.
You need not define this macro if it would always have the value
of zero.
`TRULY_NOOP_TRUNCATION (OUTPREC, INPREC)'
A C expression which is nonzero if on this machine it is safe to
"convert" an integer of INPREC bits to one of OUTPREC bits (where
OUTPREC is smaller than INPREC) by merely operating on it as if it
had only OUTPREC bits.
On many machines, this expression can be 1.
When `TRULY_NOOP_TRUNCATION' returns 1 for a pair of sizes for
modes for which `MODES_TIEABLE_P' is 0, suboptimal code can result.
If this is the case, making `TRULY_NOOP_TRUNCATION' return 0 in
such cases may improve things.
`STORE_FLAG_VALUE'
A C expression describing the value returned by a comparison
operator with an integral mode and stored by a store-flag
instruction (`sCOND') when the condition is true. This
description must apply to *all* the `sCOND' patterns and all the
comparison operators whose results have a `MODE_INT' mode.
A value of 1 or -1 means that the instruction implementing the
comparison operator returns exactly 1 or -1 when the comparison is
true and 0 when the comparison is false. Otherwise, the value
indicates which bits of the result are guaranteed to be 1 when the
comparison is true. This value is interpreted in the mode of the
comparison operation, which is given by the mode of the first
operand in the `sCOND' pattern. Either the low bit or the sign
bit of `STORE_FLAG_VALUE' be on. Presently, only those bits are
used by the compiler.
If `STORE_FLAG_VALUE' is neither 1 or -1, the compiler will
generate code that depends only on the specified bits. It can also
replace comparison operators with equivalent operations if they
cause the required bits to be set, even if the remaining bits are
undefined. For example, on a machine whose comparison operators
return an `SImode' value and where `STORE_FLAG_VALUE' is defined as
`0x80000000', saying that just the sign bit is relevant, the
expression
(ne:SI (and:SI X (const_int POWER-OF-2)) (const_int 0))
can be converted to
(ashift:SI X (const_int N))
where N is the appropriate shift count to move the bit being
tested into the sign bit.
There is no way to describe a machine that always sets the
low-order bit for a true value, but does not guarantee the value
of any other bits, but we do not know of any machine that has such
an instruction. If you are trying to port GNU CC to such a
machine, include an instruction to perform a logical-and of the
result with 1 in the pattern for the comparison operators and let
us know (*note How to Report Bugs: Bug Reporting.).
Often, a machine will have multiple instructions that obtain a
value from a comparison (or the condition codes). Here are rules
to guide the choice of value for `STORE_FLAG_VALUE', and hence the
instructions to be used:
* Use the shortest sequence that yields a valid definition for
`STORE_FLAG_VALUE'. It is more efficient for the compiler to
"normalize" the value (convert it to, e.g., 1 or 0) than for
the comparison operators to do so because there may be
opportunities to combine the normalization with other
operations.
* For equal-length sequences, use a value of 1 or -1, with -1
being slightly preferred on machines with expensive jumps and
1 preferred on other machines.
* As a second choice, choose a value of `0x80000001' if
instructions exist that set both the sign and low-order bits
but do not define the others.
* Otherwise, use a value of `0x80000000'.
Many machines can produce both the value chosen for
`STORE_FLAG_VALUE' and its negation in the same number of
instructions. On those machines, you should also define a pattern
for those cases, e.g., one matching
(set A (neg:M (ne:M B C)))
Some machines can also perform `and' or `plus' operations on
condition code values with less instructions than the corresponding
`sCOND' insn followed by `and' or `plus'. On those machines,
define the appropriate patterns. Use the names `incscc' and
`decscc', respectively, for the patterns which perform `plus' or
`minus' operations on condition code values. See `rs6000.md' for
some examples. The GNU Superoptizer can be used to find such
instruction sequences on other machines.
You need not define `STORE_FLAG_VALUE' if the machine has no
store-flag instructions.
`FLOAT_STORE_FLAG_VALUE'
A C expression that gives a non-zero floating point value that is
returned when comparison operators with floating-point results are
true. Define this macro on machine that have comparison
operations that return floating-point values. If there are no
such operations, do not define this macro.
`Pmode'
An alias for the machine mode for pointers. On most machines,
define this to be the integer mode corresponding to the width of a
hardware pointer; `SImode' on 32-bit machine or `DImode' on 64-bit
machines. On some machines you must define this to be one of the
partial integer modes, such as `PSImode'.
The width of `Pmode' must be at least as large as the value of
`POINTER_SIZE'. If it is not equal, you must define the macro
`POINTERS_EXTEND_UNSIGNED' to specify how pointers are extended to
`Pmode'.
`FUNCTION_MODE'
An alias for the machine mode used for memory references to
functions being called, in `call' RTL expressions. On most
machines this should be `QImode'.
`INTEGRATE_THRESHOLD (DECL)'
A C expression for the maximum number of instructions above which
the function DECL should not be inlined. DECL is a
`FUNCTION_DECL' node.
The default definition of this macro is 64 plus 8 times the number
of arguments that the function accepts. Some people think a larger
threshold should be used on RISC machines.
`SCCS_DIRECTIVE'
Define this if the preprocessor should ignore `#sccs' directives
and print no error message.
`NO_IMPLICIT_EXTERN_C'
Define this macro if the system header files support C++ as well
as C. This macro inhibits the usual method of using system header
files in C++, which is to pretend that the file's contents are
enclosed in `extern "C" {...}'.
`HANDLE_PRAGMA (STREAM, NODE)'
Define this macro if you want to implement any pragmas. If
defined, it is a C expression whose value is 1 if the pragma was
handled by the function. The argument STREAM is the stdio input
stream from which the source text can be read. NODE is the tree
node for the identifier after the `#pragma'.
It is generally a bad idea to implement new uses of `#pragma'. The
only reason to define this macro is for compatibility with other
compilers that do support `#pragma' for the sake of any user
programs which already use it.
`VALID_MACHINE_DECL_ATTRIBUTE (DECL, ATTRIBUTES, IDENTIFIER, ARGS)'
If defined, a C expression whose value is nonzero if IDENTIFIER
with arguments ARGS is a valid machine specific attribute for DECL.
The attributes in ATTRIBUTES have previously been assigned to DECL.
`VALID_MACHINE_TYPE_ATTRIBUTE (TYPE, ATTRIBUTES, IDENTIFIER, ARGS)'
If defined, a C expression whose value is nonzero if IDENTIFIER
with arguments ARGS is a valid machine specific attribute for TYPE.
The attributes in ATTRIBUTES have previously been assigned to TYPE.
`COMP_TYPE_ATTRIBUTES (TYPE1, TYPE2)'
If defined, a C expression whose value is zero if the attributes on
TYPE1 and TYPE2 are incompatible, one if they are compatible, and
two if they are nearly compatible (which causes a warning to be
generated).
`SET_DEFAULT_TYPE_ATTRIBUTES (TYPE)'
If defined, a C statement that assigns default attributes to newly
defined TYPE.
`DOLLARS_IN_IDENTIFIERS'
Define this macro to control use of the character `$' in identifier
names. 0 means `$' is not allowed by default; 1 means it is
allowed. 1 is the default; there is no need to define this macro
in that case. This macro controls the compiler proper; it does
not affect the preprocessor.
`NO_DOLLAR_IN_LABEL'
Define this macro if the assembler does not accept the character
`$' in label names. By default constructors and destructors in
G++ have `$' in the identifiers. If this macro is defined, `.' is
used instead.
`NO_DOT_IN_LABEL'
Define this macro if the assembler does not accept the character
`.' in label names. By default constructors and destructors in G++
have names that use `.'. If this macro is defined, these names
are rewritten to avoid `.'.
`DEFAULT_MAIN_RETURN'
Define this macro if the target system expects every program's
`main' function to return a standard "success" value by default
(if no other value is explicitly returned).
The definition should be a C statement (sans semicolon) to
generate the appropriate rtl instructions. It is used only when
compiling the end of `main'.
`HAVE_ATEXIT'
Define this if the target system supports the function `atexit'
from the ANSI C standard. If this is not defined, and
`INIT_SECTION_ASM_OP' is not defined, a default `exit' function
will be provided to support C++.
`EXIT_BODY'
Define this if your `exit' function needs to do something besides
calling an external function `_cleanup' before terminating with
`_exit'. The `EXIT_BODY' macro is only needed if neither
`HAVE_ATEXIT' nor `INIT_SECTION_ASM_OP' are defined.
`INSN_SETS_ARE_DELAYED (INSN)'
Define this macro as a C expression that is nonzero if it is safe
for the delay slot scheduler to place instructions in the delay
slot of INSN, even if they appear to use a resource set or
clobbered in INSN. INSN is always a `jump_insn' or an `insn'; GNU
CC knows that every `call_insn' has this behavior. On machines
where some `insn' or `jump_insn' is really a function call and
hence has this behavior, you should define this macro.
You need not define this macro if it would always return zero.
`INSN_REFERENCES_ARE_DELAYED (INSN)'
Define this macro as a C expression that is nonzero if it is safe
for the delay slot scheduler to place instructions in the delay
slot of INSN, even if they appear to set or clobber a resource
referenced in INSN. INSN is always a `jump_insn' or an `insn'.
On machines where some `insn' or `jump_insn' is really a function
call and its operands are registers whose use is actually in the
subroutine it calls, you should define this macro. Doing so
allows the delay slot scheduler to move instructions which copy
arguments into the argument registers into the delay slot of INSN.
You need not define this macro if it would always return zero.
`MACHINE_DEPENDENT_REORG (INSN)'
In rare cases, correct code generation requires extra machine
dependent processing between the second jump optimization pass and
delayed branch scheduling. On those machines, define this macro
as a C statement to act on the code starting at INSN.
`MULTIPLE_SYMBOL_SPACES'
Define this macro if in some cases global symbols from one
translation unit may not be bound to undefined symbols in another
translation unit without user intervention. For instance, under
Microsoft Windows symbols must be explicitly imported from shared
libraries (DLLs).
`GIV_SORT_CRITERION (GIV1, GIV2)'
In some cases, the strength reduction optimization pass can
produce better code if this is defined. This macro controls the
order that induction variables are combined. This macro is
particularly useful if the target has limited addressing modes.
For instance, the SH target has only positive offsets in
addresses. Thus sorting to put the smallest address first allows
the most combinations to be found.

File: gcc.info, Node: Config, Next: Fragments, Prev: Target Macros, Up: Top
The Configuration File
**********************
The configuration file `xm-MACHINE.h' contains macro definitions
that describe the machine and system on which the compiler is running,
unlike the definitions in `MACHINE.h', which describe the machine for
which the compiler is producing output. Most of the values in
`xm-MACHINE.h' are actually the same on all machines that GNU CC runs
on, so large parts of all configuration files are identical. But there
are some macros that vary:
`USG'
Define this macro if the host system is System V.
`VMS'
Define this macro if the host system is VMS.
`FATAL_EXIT_CODE'
A C expression for the status code to be returned when the compiler
exits after serious errors.
`SUCCESS_EXIT_CODE'
A C expression for the status code to be returned when the compiler
exits without serious errors.
`HOST_WORDS_BIG_ENDIAN'
Defined if the host machine stores words of multi-word values in
big-endian order. (GNU CC does not depend on the host byte
ordering within a word.)
`HOST_FLOAT_WORDS_BIG_ENDIAN'
Define this macro to be 1 if the host machine stores `DFmode',
`XFmode' or `TFmode' floating point numbers in memory with the
word containing the sign bit at the lowest address; otherwise,
define it to be zero.
This macro need not be defined if the ordering is the same as for
multi-word integers.
`HOST_FLOAT_FORMAT'
A numeric code distinguishing the floating point format for the
host machine. See `TARGET_FLOAT_FORMAT' in *Note Storage Layout::
for the alternatives and default.
`HOST_BITS_PER_CHAR'
A C expression for the number of bits in `char' on the host
machine.
`HOST_BITS_PER_SHORT'
A C expression for the number of bits in `short' on the host
machine.
`HOST_BITS_PER_INT'
A C expression for the number of bits in `int' on the host machine.
`HOST_BITS_PER_LONG'
A C expression for the number of bits in `long' on the host
machine.
`ONLY_INT_FIELDS'
Define this macro to indicate that the host compiler only supports
`int' bit fields, rather than other integral types, including
`enum', as do most C compilers.
`OBSTACK_CHUNK_SIZE'
A C expression for the size of ordinary obstack chunks. If you
don't define this, a usually-reasonable default is used.
`OBSTACK_CHUNK_ALLOC'
The function used to allocate obstack chunks. If you don't define
this, `xmalloc' is used.
`OBSTACK_CHUNK_FREE'
The function used to free obstack chunks. If you don't define
this, `free' is used.
`USE_C_ALLOCA'
Define this macro to indicate that the compiler is running with the
`alloca' implemented in C. This version of `alloca' can be found
in the file `alloca.c'; to use it, you must also alter the
`Makefile' variable `ALLOCA'. (This is done automatically for the
systems on which we know it is needed.)
If you do define this macro, you should probably do it as follows:
#ifndef __GNUC__
#define USE_C_ALLOCA
#else
#define alloca __builtin_alloca
#endif
so that when the compiler is compiled with GNU CC it uses the more
efficient built-in `alloca' function.
`FUNCTION_CONVERSION_BUG'
Define this macro to indicate that the host compiler does not
properly handle converting a function value to a
pointer-to-function when it is used in an expression.
`MULTIBYTE_CHARS'
Define this macro to enable support for multibyte characters in the
input to GNU CC. This requires that the host system support the
ANSI C library functions for converting multibyte characters to
wide characters.
`POSIX'
Define this if your system is POSIX.1 compliant.
`NO_SYS_SIGLIST'
Define this if your system *does not* provide the variable
`sys_siglist'.
Some systems do provide this variable, but with a different name
such as `_sys_siglist'. On these systems, you can define
`sys_siglist' as a macro which expands into the name actually
provided.
Autoconf normally defines `SYS_SIGLIST_DECLARED' when it finds a
declaration of `sys_siglist' in the system header files. However,
when you define `sys_siglist' to a different name autoconf will
not automatically define `SYS_SIGLIST_DECLARED'. Therefore, if
you define `sys_siglist', you should also define
`SYS_SIGLIST_DECLARED'.
`USE_PROTOTYPES'
Define this to be 1 if you know that the host compiler supports
prototypes, even if it doesn't define __STDC__, or define it to be
0 if you do not want any prototypes used in compiling GNU CC. If
`USE_PROTOTYPES' is not defined, it will be determined
automatically whether your compiler supports prototypes by
checking if `__STDC__' is defined.
`NO_MD_PROTOTYPES'
Define this if you wish suppression of prototypes generated from
the machine description file, but to use other prototypes within
GNU CC. If `USE_PROTOTYPES' is defined to be 0, or the host
compiler does not support prototypes, this macro has no effect.
`MD_CALL_PROTOTYPES'
Define this if you wish to generate prototypes for the `gen_call'
or `gen_call_value' functions generated from the machine
description file. If `USE_PROTOTYPES' is defined to be 0, or the
host compiler does not support prototypes, or `NO_MD_PROTOTYPES'
is defined, this macro has no effect. As soon as all of the
machine descriptions are modified to have the appropriate number
of arguments, this macro will be removed.
`NO_STAB_H'
Define this if your system does not have the include file
`stab.h'. If `USG' is defined, `NO_STAB_H' is assumed.
`PATH_SEPARATOR'
Define this macro to be a C character constant representing the
character used to separate components in paths. The default value
is the colon character
`DIR_SEPARATOR'
If your system uses some character other than slash to separate
directory names within a file specification, define this macro to
be a C character constant specifying that character. When GNU CC
displays file names, the character you specify will be used. GNU
CC will test for both slash and the character you specify when
parsing filenames.
`OBJECT_SUFFIX'
Define this macro to be a C string representing the suffix for
object files on your machine. If you do not define this macro,
GNU CC will use `.o' as the suffix for object files.
`EXECUTABLE_SUFFIX'
Define this macro to be a C string representing the suffix for
executable files on your machine. If you do not define this
macro, GNU CC will use the null string as the suffix for object
files.
`COLLECT_EXPORT_LIST'
If defined, `collect2' will scan the individual object files
specified on its command line and create an export list for the
linker. Define this macro for systems like AIX, where the linker
discards object files that are not referenced from `main' and uses
export lists.
In addition, configuration files for system V define `bcopy',
`bzero' and `bcmp' as aliases. Some files define `alloca' as a macro
when compiled with GNU CC, in order to take advantage of the benefit of
GNU CC's built-in `alloca'.

File: gcc.info, Node: Fragments, Next: Funding, Prev: Config, Up: Top
Makefile Fragments
******************
When you configure GNU CC using the `configure' script (*note
Installation::.), it will construct the file `Makefile' from the
template file `Makefile.in'. When it does this, it will incorporate
makefile fragment files from the `config' directory, named `t-TARGET'
and `x-HOST'. If these files do not exist, it means nothing needs to
be added for a given target or host.
* Menu:
* Target Fragment:: Writing the `t-TARGET' file.
* Host Fragment:: Writing the `x-HOST' file.

File: gcc.info, Node: Target Fragment, Next: Host Fragment, Up: Fragments
The Target Makefile Fragment
============================
The target makefile fragment, `t-TARGET', defines special target
dependent variables and targets used in the `Makefile':
`LIBGCC1'
The rule to use to build `libgcc1.a'. If your target does not
need to use the functions in `libgcc1.a', set this to empty.
*Note Interface::.
`CROSS_LIBGCC1'
The rule to use to build `libgcc1.a' when building a cross
compiler. If your target does not need to use the functions in
`libgcc1.a', set this to empty. *Note Cross Runtime::.
`LIBGCC2_CFLAGS'
Compiler flags to use when compiling `libgcc2.c'.
`LIB2FUNCS_EXTRA'
A list of source file names to be compiled or assembled and
inserted into `libgcc.a'.
`CRTSTUFF_T_CFLAGS'
Special flags used when compiling `crtstuff.c'. *Note
Initialization::.
`CRTSTUFF_T_CFLAGS_S'
Special flags used when compiling `crtstuff.c' for shared linking.
Used if you use `crtbeginS.o' and `crtendS.o' in `EXTRA-PARTS'.
*Note Initialization::.
`MULTILIB_OPTIONS'
For some targets, invoking GNU CC in different ways produces
objects that can not be linked together. For example, for some
targets GNU CC produces both big and little endian code. For
these targets, you must arrange for multiple versions of
`libgcc.a' to be compiled, one for each set of incompatible
options. When GNU CC invokes the linker, it arranges to link in
the right version of `libgcc.a', based on the command line options
used.
The `MULTILIB_OPTIONS' macro lists the set of options for which
special versions of `libgcc.a' must be built. Write options that
are mutually incompatible side by side, separated by a slash.
Write options that may be used together separated by a space. The
build procedure will build all combinations of compatible options.
For example, if you set `MULTILIB_OPTIONS' to `m68000/m68020
msoft-float', `Makefile' will build special versions of `libgcc.a'
using the sets of options `-m68000', `-m68020', `-msoft-float',
`-m68000 -msoft-float', and `-m68020 -msoft-float'.
`MULTILIB_DIRNAMES'
If `MULTILIB_OPTIONS' is used, this variable specifies the
directory names that should be used to hold the various libraries.
Write one element in `MULTILIB_DIRNAMES' for each element in
`MULTILIB_OPTIONS'. If `MULTILIB_DIRNAMES' is not used, the
default value will be `MULTILIB_OPTIONS', with all slashes treated
as spaces.
For example, if `MULTILIB_OPTIONS' is specified as `m68000/m68020
msoft-float', then the default value of `MULTILIB_DIRNAMES' is
`m68000 m68020 msoft-float'. You may specify a different value if
you desire a different set of directory names.
`MULTILIB_MATCHES'
Sometimes the same option may be written in two different ways.
If an option is listed in `MULTILIB_OPTIONS', GNU CC needs to know
about any synonyms. In that case, set `MULTILIB_MATCHES' to a
list of items of the form `option=option' to describe all relevant
synonyms. For example, `m68000=mc68000 m68020=mc68020'.
`MULTILIB_EXCEPTIONS'
Sometimes when there are multiple sets of `MULTILIB_OPTIONS' being
specified, there are combinations that should not be built. In
that case, set `MULTILIB_EXCEPTIONS' to be all of the switch
exceptions in shell case syntax that should not be built.
For example, in the PowerPC embedded ABI support, it was not
desirable to build libraries that compiled with the
`-mcall-aixdesc' option and either of the `-mcall-aixdesc' or
`-mlittle' options at the same time, and therefore
`MULTILIB_EXCEPTIONS' is set to `*mrelocatable/*mcall-aixdesc*
*mlittle/*mcall-aixdesc*'.
`MULTILIB_EXTRA_OPTS'
Sometimes it is desirable that when building multiple versions of
`libgcc.a' certain options should always be passed on to the
compiler. In that case, set `MULTILIB_EXTRA_OPTS' to be the list
of options to be used for all builds.

File: gcc.info, Node: Host Fragment, Prev: Target Fragment, Up: Fragments
The Host Makefile Fragment
==========================
The host makefile fragment, `x-HOST', defines special host dependent
variables and targets used in the `Makefile':
`CC'
The compiler to use when building the first stage.
`CLIB'
Additional host libraries to link with.
`OLDCC'
The compiler to use when building `libgcc1.a' for a native
compilation.
`OLDAR'
The version of `ar' to use when building `libgcc1.a' for a native
compilation.
`INSTALL'
The install program to use.

File: gcc.info, Node: Funding, Next: Look and Feel, Prev: Fragments, Up: Top
Funding Free Software
*********************
If you want to have more free software a few years from now, it makes
sense for you to help encourage people to contribute funds for its
development. The most effective approach known is to encourage
commercial redistributors to donate.
Users of free software systems can boost the pace of development by
encouraging for-a-fee distributors to donate part of their selling price
to free software developers--the Free Software Foundation, and others.
The way to convince distributors to do this is to demand it and
expect it from them. So when you compare distributors, judge them
partly by how much they give to free software development. Show
distributors they must compete to be the one who gives the most.
To make this approach work, you must insist on numbers that you can
compare, such as, "We will donate ten dollars to the Frobnitz project
for each disk sold." Don't be satisfied with a vague promise, such as
"A portion of the profits are donated," since it doesn't give a basis
for comparison.
Even a precise fraction "of the profits from this disk" is not very
meaningful, since creative accounting and unrelated business decisions
can greatly alter what fraction of the sales price counts as profit.
If the price you pay is $50, ten percent of the profit is probably less
than a dollar; it might be a few cents, or nothing at all.
Some redistributors do development work themselves. This is useful
too; but to keep everyone honest, you need to inquire how much they do,
and what kind. Some kinds of development make much more long-term
difference than others. For example, maintaining a separate version of
a program contributes very little; maintaining the standard version of a
program for the whole community contributes much. Easy new ports
contribute little, since someone else would surely do them; difficult
ports such as adding a new CPU to the GNU C compiler contribute more;
major new features or packages contribute the most.
By establishing the idea that supporting further development is "the
proper thing to do" when distributing free software for a fee, we can
assure a steady flow of resources into making more free software.
Copyright (C) 1994 Free Software Foundation, Inc.
Verbatim copying and redistribution of this section is permitted
without royalty; alteration is not permitted.

File: gcc.info, Node: Look and Feel, Next: Copying, Prev: Funding, Up: Top
Protect Your Freedom--Fight "Look And Feel"
*******************************************
This section is a political message from the League for Programming
Freedom to the users of GNU CC. We have included it here because
the issue of interface copyright is important to the GNU project.
Apple, Lotus, and now CDC have tried to create a new form of legal
monopoly: a copyright on a user interface.
An interface is a kind of language--a set of conventions for
communication between two entities, human or machine. Until a few years
ago, the law seemed clear: interfaces were outside the domain of
copyright, so programmers could program freely and implement whatever
interface the users demanded. Imitating de-facto standard interfaces,
sometimes with improvements, was standard practice in the computer
field. These improvements, if accepted by the users, caught on and
became the norm; in this way, much progress took place.
Computer users, and most software developers, were happy with this
state of affairs. However, large companies such as Apple and Lotus
would prefer a different system--one in which they can own interfaces
and thereby rid themselves of all serious competitors. They hope that
interface copyright will give them, in effect, monopolies on major
classes of software.
Other large companies such as IBM and Digital also favor interface
monopolies, for the same reason: if languages become property, they
expect to own many de-facto standard languages. But Apple and Lotus are
the ones who have actually sued. Apple's lawsuit was defeated, for
reasons only partly related to the general issue of interface copyright.
Lotus won lawsuits against two small companies, which were thus put
out of business. Then Lotus sued Borland; Lotus won in the trial court
(no surprise, since it was the same court that had ruled for Lotus twice
before), but the court of appeals ruled in favor of Borland, which was
assisted by a friend-of-the-court brief from the League for Programming
Freedom.
Lotus appealed the case to the Supreme Court, which heard the case
but was unable to reach a decision. This failure means that the appeals
court decision stands, in one portion of the United States, and may
influence the other appeals courts, but it does not set a nationwide
precedent. The battle is not over, and it is not limited to the United
States.
The battle is extending into other areas of software as well. In
1995 a company that produced a simulator for a CDC computer was shut
down by a copyright lawsuit, in which CDC charged that the simulator
infringed the copyright on the manuals for the computer.
If the monopolists get their way, they will hobble the software
field:
* Gratuitous incompatibilities will burden users. Imagine if each
car manufacturer had to design a different way to start, stop, and
steer a car.
* Users will be "locked in" to whichever interface they learn; then
they will be prisoners of one supplier, who will charge a
monopolistic price.
* Large companies have an unfair advantage wherever lawsuits become
commonplace. Since they can afford to sue, they can intimidate
smaller developers with threats even when they don't really have a
case.
* Interface improvements will come slower, since incremental
evolution through creative partial imitation will no longer occur.
If interface monopolies are accepted, other large companies are
waiting to grab theirs:
* Adobe is expected to claim a monopoly on the interfaces of various
popular application programs, if Lotus ultimately wins the case
against Borland.
* Open Computing magazine reported a Microsoft vice president as
threatening to sue people who imitate the interface of Windows.
Users invest a great deal of time and money in learning to use
computer interfaces. Far more, in fact, than software developers
invest in developing *and even implementing* the interfaces. Whoever
can own an interface, has made its users into captives, and
misappropriated their investment.
To protect our freedom from monopolies like these, a group of
programmers and users have formed a grass-roots political organization,
the League for Programming Freedom.
The purpose of the League is to oppose monopolistic practices such as
interface copyright and software patents. The League calls for a return
to the legal policies of the recent past, in which programmers could
program freely. The League is not concerned with free software as an
issue, and is not affiliated with the Free Software Foundation.
The League's activities include publicizing the issues, as is being
done here, and filing friend-of-the-court briefs on behalf of
defendants sued by monopolists.
The League's membership rolls include Donald Knuth, the foremost
authority on algorithms, John McCarthy, inventor of Lisp, Marvin Minsky,
founder of the MIT Artificial Intelligence lab, Guy L. Steele, Jr.,
author of well-known books on Lisp and C, as well as Richard Stallman,
the developer of GNU CC. Please join and add your name to the list.
Membership dues in the League are $42 per year for programmers, managers
and professionals; $10.50 for students; $21 for others.
Activist members are especially important, but members who have no
time to give are also important. Surveys at major ACM conferences have
indicated a vast majority of attendees agree with the League on both
issues (interface copyrights and software patents). If just ten percent
of the programmers who agree with the League join the League, we will
probably triumph.
To join, or for more information, send electronic mail to the
address `lpf@uunet.uu.net' or write to:
League for Programming Freedom
1 Kendall Square #143
P.O. Box 9171
Cambridge, MA 02139
In addition to joining the League, here are some suggestions from the
League for other things you can do to protect your freedom to write
programs:
* Tell your friends and colleagues about this issue and how it
threatens to ruin the computer industry.
* Mention that you are a League member in your `.signature', and
mention the League's email address for inquiries.
* Ask the companies you consider working for or working with to make
statements against software monopolies, and give preference to
those that do.
* When employers ask you to sign contracts giving them copyright on
your work, insist on a clause saying they will not claim the
copyright covers imitating the interface.
* When employers ask you to sign contracts giving them patent rights,
insist on clauses saying they can use these rights only
defensively. Don't rely on "company policy," since that can
change at any time; don't rely on an individual executive's
private word, since that person may be replaced. Get a commitment
just as binding as the commitment they get from you.
* Write to Congress to explain the importance of these issues.
House Subcommittee on Intellectual Property
2137 Rayburn Bldg
Washington, DC 20515
Senate Subcommittee on Patents, Trademarks and Copyrights
United States Senate
Washington, DC 20510
(These committees have received lots of mail already; let's give
them even more.)
Democracy means nothing if you don't use it. Stand up and be
counted!